Liquid crystal display devices (LCDs) used for devices such as television, personal computers, and cell phones display a visual image by controlling the transmission amount of emitted light from a light source with the use of a liquid crystal panel that includes a pair of polarizing plates disposed on the both sides of a liquid crystal cell. The polarizing plates attached to the liquid crystal cell are commonly absorption-type polarizing plates, or photoabsorption-type dichroic linear polarizing plates as they are often called. Polarizing plates that use triacetyl cellulose (TAC) for the protection of iodine-containing PVA are widely used.
The absorption-type polarizing plates pass polarized light of the polarization direction along the transmission axis, and absorb most of the polarized light orthogonal to the transmission axis. Because close to 50% of the unpolarized light emitted by a light source unit is absorbed by the absorption-type polarizing plates, the efficiency of using light is poor, as has been pointed out in the past. For more effective use of polarized light orthogonal to the transmission axis, there have been studies of a configuration, referred to by the common name brightness enhancement film, that uses a reflection-type polarizer between a light source and a liquid crystal panel. One example of such a reflection-type polarizer is a polymer-type film that takes advantage of optical interference (see, for example, Patent Document 1).
Concerning the polarizing plates attached to a liquid crystal cell, various laminate configurations have also been studied in which an absorption-type polarizing plate and a reflection-type polarizing plate are combined according to, for example, the type of the light used for the display device, and the intended use of the display device, such as in a reflection display that makes use of outside light, and a transmission display that uses a backlight.
For example, Patent Document 2 discloses a liquid crystal display device in which an electric field is applied to the liquid crystal layer to vary the retardation value of the liquid crystal and shift the retardation of the incident polarized light on the liquid crystal layer by a certain amount. As an example of the polarizing plates used on the both sides of the liquid crystal layer, the publication describes a reflection-type polarizing plate of a planar multilayer structure provided on the side of the light source and that includes three or more layers of films having birefringence, and an absorption-type polarizing plate provided on the opposite side relative to the liquid crystal layer.
Patent Document 3 describes solving the warping of polarizing plates caused by the difference in the extent of temperature-dependent expansion and contraction of an absorption-type polarizing plate and a reflection-type polarizing plate disposed on the both sides of a liquid crystal cell that includes a liquid crystal between flexible substrates. The publication proposes solving the warping by combining these polarizing plates in a specific laminate configuration. The publication also discloses a birefringent dielectric multilayer film, specifically a brightness enhancement film, as an example of the reflection-type polarizing plate.
For example, patent documents 4 to 6 disclose reflective polarizing polymer films of a birefringent multilayer configuration, specifically films that function to reflect polarized light of one direction, and pass polarized light of another direction.
If the absorption-type polarizing plate used as the polarizing plate attached to the liquid crystal cell were to be replaced solely by a reflection-type polarizing plate of a multilayer configuration, the reflection-type polarizing plate needs to have a degree of polarization comparative to that of the absorption-type polarizing plate.    Patent Document 1: JP-T-09-507308 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)    Patent Document 2: JP-A-2005-316511    Patent Document 3: JP-A-2009-103817    Patent Document 4: JP-A-04-268505    Patent Document 5: JP-T-9-506837    Patent Document 6: WO2001/47711